The present invention relates to an infinitely adjustable cone disc transmission including two pairs of cone discs arranged on the driving and driven shafts as well as a transfer means rotating between the pairs of discs, with the cone discs being fixed to rotate with the shaft carrying them. On each shaft one cone disc is also axially fixed while the associated second cone disc is configured as an axially displaceable component of a cylinder-piston unit that is fixed to the shaft and to which pressure medium is supplied through an inlet from a four-edged spool valve. The latter is adjustable by means of an adjustment member and, in order to press on the transfer means and to set and maintain the transmission ratio, is provided with an outlet for the outgoing pressure medium. A discharge conduit is connected to the pressure medium outlet, with at least one torque sensor being disposed therein. This torque sensor is arranged on one of the transmission shafts in the flow of moments at that location and influences, as a function of the load, the pressure medium pressure in the cylinder-piston units. The torque sensor is hydraulically connected in series with an adjustable pressurizing valve with which the pressure medium pressure can be additionally influenced.
Such a transmission is disclosed, for example, in German Patent 3,743,195. In that patent, a torque sensor disposed on the driving side is hydraulically followed by a pressurizing valve that additionally influences the pressure medium pressure exclusively as a function of the transmission ratio of the power train in such a way that, with an increasing transmission ratio of driving revolutions to driven revolutions, this pressure increases as well.
This pressure medium pressure is furnished by a pump, with the energy consumption of this pump for a constant conveyed stream being approximately proportional to the pressure medium pressure that it must furnish. Since the energy to be expended for operation of the pump and the friction losses as a function of contact pressure in the drive loop have a negative influence on the overall efficiency of the transmission, it is desirable to keep the pressure level as low as possible in dependence on the load state. This is relevant particularly under partial load, that is, in connection with motor vehicles, particularly in city traffic.
However, in the transmission described in German Patent 3,743,195, the result is that the pressure medium pressure may possibly be kept very high even if the load applied to the transmission is small, because the pressurizing valve operates purely as a function of the transmission ratio, particularly if the load is small but the transmission ratio is high at the same time.